Systems and methods for high humidity curing within tablet coating system

ABSTRACT

The disclosure encompasses systems and methods for performing high temperature and high humidity curing of tablets using air flow delivered from a recirculating air handler to a pan coater of a tablet coating device. The recirculating air handler may be integrated into a preexisting tablet coating device so that the air flow may be delivered by the preexisting air handler or by the recirculating air handler as desired.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/549,151, filed Aug. 23, 2019, now issued as U.S. Pat. No. 11,077,024,which is a continuation of U.S. application Ser. No. 15/568,587, filedOct. 23, 2017, now issued as U.S. Pat. No. 10,441,508, which claimspriority to PCT Application No. PCT/US2015/027558, filed Apr. 24, 2015,the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The formulations of a variety of active pharmaceutical compounds makeuse of a wide range of polymer coatings such as enteric coatings andother release-modifying coatings to produce a formulation with a desiredrelease profile. These coating materials, which are typically polymercompositions, may be applied as one or more film coatings over a coretablet under controlled conditions to produce a modified-releaseformulation that may include the tablet covered with one or more layersof different polymer compositions.

Existing tablet coating systems typically include a pan coater used toapply the film coatings to tablet cores to form pharmaceuticalcompositions. The pan coater may include a coating pan or perforatedrotating drum that rotates within the controlled environment inside acabinet. Within the cabinet, a spraying system may pump a fine mist ofcoating solution toward tablets within the coating pan under controlledconditions to form a thin film the coating on the tablets. Thecontrolled conditions within the cabinet containing the coating panresult in the solvent portion of the coating solution to rapidlyevaporate upon contact with the surface of the tablets, leaving behindthe solids portion of the coating solution to form the coating.

The properties of the coated tablets are highly sensitive to variationsin the operational parameters of the spraying system as well as thecontrolled conditions within the cabinet. Typically, the controlledconditions within the cabinet include elevated temperature and lowhumidity to facilitate the rapid evaporation of the coating solution. Tothis end, an air handling unit may deliver heated and dehumidified airinto the cabinet, where it passes over the tablets within the coatingpan and subsequently exhausts out a separate exhaust. This one-wayairflow provides a low-humidity heated airflow to dry the tablets, andalso transports unused coating solution out of the coating pan via theexhaust flow to provide additional control over the coating process.

To complete the production of coated tablet compositions, the coatedtablets may be subjected to an additional curing process to allow thepolymer coating to fully cure into a particular form to impart thedesired coating properties, such as coating smoothness or pH-dependentsolubility. In some cases, the curing process may include exposing thecoated tablets to a particular temperature profile for a predeterminedtime period. In these cases, the additional curing process may beperformed within the pan coater. However, for certain polymer materials,the curing process may require process conditions that extend beyond thecapabilities of existing pan coaters.

One type of tablet formulation may include ingredients that require anadditional curing process conducted at relatively high humidity toimpart the desired coating properties. High humidity conditions are atodds with typical tablet coating conditions. In fact, many defects intablet coating processes, such as picking, sticking, erosion, peeling,and/or frosting are attributed to inadequate drying of the coatedtablets, which may in part be attributed to humid coating conditions.Thus, in order to perform a high humidity curing process, coated tabletsmay be removed to a separate curing chamber for exposure to highhumidity as needed. However, transferring the uncured coated tablets toa separate curing chamber may impact tablet quality by exposing thetablets to undesired temperature, humidity and/or mechanical damageduring transfer. In addition, the transfer to a separate curing chambermay add additional time and cost to the manufacturing process.

A need exists in the art for a process and method of providing highhumidity conditions within an existing pan coater device. Such a processand method may also enhance the quality, production time and productioncosts of tablet coatings cured at high humidity conditions.

SUMMARY OF THE INVENTION

In one aspect a recirculating air handler for supplying high humidityair flow to a pan coater of a tablet coating system is provided. Therecycling air handler includes: a humidifier to introduce moisture intothe air flow in an amount resulting in a relative humidity in the airflow of up to about 90%; and a vent to release air from therecirculating air handler to the atmosphere via a vent valve. The ventvalve may be opened as needed to maintain the pressure within the pancoater to at least 0.15 inches of water column below atmosphericpressure. The recirculating air handler may further include at least oneinlet filter situated upstream of the humidifier to remove particulatematter from an airflow entering the recirculating air handler and atleast one exit filter situated downstream of the of the humidifier toremove particulate matter from an airflow exiting the pan coater. Therecirculating air handler may further include at least one drain pan.The at least one drain pan may include one or more of: an inlet drainpan situated upstream of the humidifier and at least one filter toremove any condensation formed out of the exhaust air delivered from thepan coater; and an outlet drain pan to remove any condensation formedout of the exit air to be delivered to the pan coater. The outlet drainpan may be situated downstream of the humidifier and a portion of theoutlet drain pan may extend upstream of the humidifier. Therecirculating air handler may further include: a supply air ductcomprising a supply end operatively connected to supply air to the pancoater and an exit end opposite to the supply end and operativelyconnected to the exit of the recirculating air handler; and an exhaustduct comprising an exhaust end operatively connected to receive exhaustfrom the pan coater and an inlet end opposite to the exhaust end andoperatively connected to the inlet of the recirculating air handler.

In another aspect, a tablet coating system to apply one or more coatingsto a tablet is provided. The tablet coating system includes: arecirculating air handler to supply a humid air flow to a pan coater; aflow-through air handler to supply a low humidity air flow to the pancoater; and one or more ducts and one or more configurable valves. Therecirculating air handler includes: a humidifier to introduce watervapor into the air flow in an amount resulting in a relative humidity inthe air flow of up to about 90%; and a vent to release air from therecirculating air handler to the atmosphere via a vent valve. The ventvalve is opened as needed to maintain an air pressure within the pancoater of at least 0.15 inches of water column below atmosphericpressure. The one or more configurable valves may be configured to: cutoff flow through the recirculating air handler and direct the air flowfrom the flow-through air handler to a supply of the pan coater and froman exhaust of the pan coater to an exhaust stack; or cut off flow fromthe flow-through air handler and direct the air flow from an exit of therecirculating air handler to a supply of the pan coater and from theexhaust of the pan coater to an inlet of the flow-through air handler.The tablet coating system may also include at least one inlet filtersituated upstream of the humidifier to remove particulate matter from anairflow entering the recirculating air handler and at least one exitfilter situated downstream of the of the humidifier to removeparticulate matter from an airflow exiting the recirculating airhandler. The tablet coating system may further include at least onedrain pan. The at least one drain pan may include one or more of: aninlet drain pan situated upstream of the humidifier and at least onefilter to remove any condensation formed out of the exhaust airdelivered from the pan coater; and an exit drain pan to remove anycondensation formed out of the exit air to be delivered to the pancoater. The exit drain pan may be situated downstream of the humidifierand a portion of the exit drain pan may extend upstream of thehumidifier. The one or more ducts may include: a supply duct thatincludes a supply end operatively connected to supply air to the pancoater and an exit end opposite to the supply end and operativelyconnected to the exit of the recirculating air handler; an exhaust ductcomprising an exhaust end operatively connected to receive exhaust fromthe pan coater and an inlet end opposite to the exhaust end andoperatively connected to the inlet of the recirculating air handler; anexhaust stack operatively connected to the exhaust duct between theexhaust end and the inlet end at one end and venting to the atmosphereat an opposite end; and a second supply duct operatively connected at afirst end to an exit end of the flow-through air handler and operativelyconnected at a second end to the supply duct between the supply end andthe exit end. The one or more valves may include: a first valve situatedwithin the supply duct near the exit end; a second valve situated withinthe exhaust duct near the inlet end; a third valve situated within theexhaust stack; and a fourth valve situated within the second supplyduct. The first and second valves may be opened and the third and fourthvalve may be closed to supply the pan coater with humid air flow fromthe recirculating air handler; or the first and second valves may beclosed and the third and fourth valves may be opened to supply the pancoater with low-humidity air flow from the flow-through air handler.

In an additional aspect, a method of supplying a humid air flow to a pancoater of a tablet coating system is provided. The method may include:establishing an air flow through a recirculating air handler operativelyconnected to receive exhaust air flow from the pan coater and to delivera supply air flow to the pan coater; heating the air flow to pre-heatthe pan coater, a supply duct delivering air flow to the pan coater, andan exhaust duct receiving exhaust flow from the pan coater; establishingand maintaining humid air flow within the pan coater for a duration of ahumidification process; and clearing the humid air flow from pan coater.The air flow may be heated to a temperature ranging from about 50° C. toabout 80° C. and a dew point ranging from about 45° C. to about 55° C.The humid air flow may be maintained at a humidity of up to about 90%relative humidity. The humid air flow may be produced by clean steamintroduced into the flow from a humidifier situated within therecirculating air handler. The method may further include maintaining apressure within the pan coater that is at least 0.15 inches of watercolumn below atmospheric pressure. The pressure within the pan coatermay be maintained by venting air flow from the recirculating air handlerto the atmosphere as needed. The method may further include filteringparticulate matter from the air flow received by the recirculating airhandler by directing the airflow through one or more filters situatedwithin the recirculating air handler. The humid air flow may be clearedfrom the pan coater by deactivating the humidifier and maintaining apressure within the pan coater that is at least 0.25 inches of watercolumn below atmospheric pressure. The method may further includereestablishing air flow through a flow-through air handler operativelyconnected to the supply duct and configured to receive external air fromthe atmosphere. Reestablishing air flow through the flow-through airhandler may include blocking flow entering and exiting the recirculatingair handler, opening flow from the flow-through air handler into thesupply duct, and directing the exhaust flow from the pan coater throughan exhaust stack into the atmosphere. The humid air flow may be providedto the pan coater with essentially no formation of condensation.

FIELD OF THE INVENTION

The disclosure encompasses systems and methods for performing hightemperature and high humidity curing of tablets using a recirculatingair handler integrated into a preexisting tablet coating system.

DESCRIPTION OF FIGURES

The following figures illustrate various aspects of the disclosure.

FIG. 1 is a block diagram illustrating the components of a tabletcoating system modified with a recirculating air handler in one aspect.

FIG. 2 is a block diagram illustrating the components of the modifiedtablet coating system of FIG. 1 operating in a preexisting mode in whichthe pan coater airflow is supplied by a flow-through air handler.

FIG. 3 is a block diagram illustrating the components of the modifiedtablet coating system of FIG. 1 operating in a humidification mode inwhich the pan coater airflow is supplied by the recirculating airhandler.

FIG. 4 is a block diagram illustrating the components of a recirculatingair handler in an aspect.

FIG. 5 is a flow chart illustrating the steps of a method to providehumid airflow to the pan coater of a tablet coating device as one stageof a tablet coating procedure in an aspect.

FIG. 6 is a block diagram illustrating the integration of the modules ofa control system with the components of a tablet coating system, inparticular the control of one or more valves of the system by the modecontrol module.

FIG. 7 is a block diagram illustrating the integration of the modules ofa control system with the components of a tablet coating system, inparticular the control of the venting valve by the P-stat module andassociated pressure sensors.

FIG. 8 is a block diagram illustrating the integration of the modules ofa control system with the components of a tablet coating system, inparticular the monitoring of filter conditions by the filter monitormodule and associated pressure sensors.

FIG. 9 is a block diagram illustrating the integration of the modules ofa control system with the components of a tablet coating system, inparticular the control of the air heater by the T-stat module andassociated temperature sensors.

FIG. 10 is a block diagram illustrating the integration of the modulesof a control system with the components of a tablet coating system, inparticular the control of the air humidifier by the H-stat module andassociated humidity sensors.

FIG. 11 is a block diagram illustrating the integration of the modulesof a control system with the components of a tablet coating system, inparticular the control of the air blower by the V-stat module andassociated air flow sensors.

Other aspects and iterations of the invention are described in moredetail below.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that a tablet coating device may be modified toinclude a recirculating air handler capable of delivering relativelyhigh temperature and high humidity air to the pan coater of the tabletcoating device for use in one or more tablet curing processes withminimal impact on the pan coater's preexisting capabilities. Therecirculating air handler may be integrated into the duct and controlsystems of an existing tablet coating system and may be operated in amanner similar to the operation of the existing tablet coating system.

FIG. 1 is a block diagram illustrating a tablet coating system 100modified to incorporate a recirculating air handler 106. In this system100, air is delivered to a pan coater 102 via a supply duct 110 andexits the pan coater 102 via an exhaust duct 108. The air delivered tothe pan coater may be conditioned to a preselected temperature andhumidity using either a flow-through air handler 104 or a recirculatingair handler 106 depending on the desired process to be conducted withinthe pan coater 102. The selection of the flow-through air handler or therecirculating air handler for conditioning of the air introduced intothe pan coater 102 may be implemented via valves 112, 114, 116, and 118situated within the ducting of the system 100.

Any suitable fluid control device known in the art may be selected foruse as a valve in the system 100. In one aspect, any known type of valvemay be used including, but not limited to: a ball valve, a butterflyvalve, a gate valve, a globe valve, a needle valve, and any othersuitable valve types known in the art. In another aspect, a damper maybe selected for use as a valve in the system 100 including, but notlimited to: single blade dampers, multi-blade dampers, round dampers,louvers, and any other suitable type of damper known in the art.

As illustrated in FIG. 2 , to select the flow-through air handler foruse in a preexisting mode of operation of the tablet coating system 100,valves 114 and 116 are closed and valves 112 and 118 are opened.Atmospheric air 202 enters the flow-through air handler 104 to befiltered, heated, and/or dehumidified as needed. The conditioned air 204is directed to the pan coater 102 via the open valve 112 and isprevented from entering the recirculating air handler by the closedvalve 114. After passing through the pan coater 102, the exhaust air 206is directed out of the pan coater 102 and through the exhaust stack 126through the open valve 118; the exhaust air is prevented from enteringthe recirculating air handler by the closed valve 116. In thispreexisting mode, the tablet coating system 100 may operate with all thecapabilities of the preexisting system including, but not limited to:preheating tablets, applying one or more coatings to the tablets, anddrying the tablets.

The recirculating air handler 106 may be selected for use in ahumidification mode by closing valves 112 and 118 and opening valves 114and 116 as illustrated in FIG. 3 . Conditioned air 302 exiting therecirculating air handler 106, which may be filtered, heated, andhumidified as needed is directed into the pan coater 102 through openvalve 114 and prevented from entering the flow-through air handler 104by closed valve 112. The exhaust air 304 is recirculated through therecirculating air handler 106 via the open valve 116 and prevented fromentering the exhaust stack 126 by the closed valve 118.

The tablet coating system 100 may incorporate additional features toinhibit condensation of water from the airflow and/or to prevent anycondensed water from entering the pan coater 102. In one aspect, one ormore portions of the air ducts of the system 100 including, but notlimited to, the supply duct 110 and/or the exhaust duct 108 of the pancoater 102, the inlet duct 124 or the exit duct 122 of the recirculatingair handler 106, and any combination thereof may include insulation toreduce condensation resulting from heat losses within the ducts of thesystem 100. Any suitable insulation type may be selected to insulate theducts of the tablet coating system 100 including, but not limited toinsulating sheets, insulating wraps, foam insulation, and any otherknown insulation type.

In another aspect, the supply duct 110 and/or the exhaust duct 108 ofthe pan coater 102 may be installed in an orientation in which the ductsslope away from the pan coater 102 to inhibit the incursion of moistureformed within these ducts. In this aspect, any water condensation formedwithin each duct would travel along the downward slope of each duct,which is arranged to be away from the pan coater 102 in this aspect. Theamount of slope may be specified using any method or standard known inthe art. In one aspect, the slope may be greater than about 0.25 inchesof vertical height change for each linear foot of duct. In various otheraspects, the slope may be greater than about 0.3 inches of verticalheight change, greater than about 0.5 inches of vertical height change,greater than about 0.75 inches of vertical height change, greater thanabout 1 inch of vertical height change, greater than about 2 inches ofvertical height change, greater than about 3 inches of vertical heightchange, greater than about 4 inches of vertical height change, greaterthan about 5 inches of vertical height change, and greater than about 6inches of vertical height change.

The tablet coating system 100 as disclosed herein overcomes manylimitations of existing tablet coating systems. Due to the integrationof the recirculating air handler 106 with the existing ductwork andcontrollers of the existing tablet coating systems, the tablet coatingsystem 100 as disclosed may conduct an expanded repertoire of processsteps 10 within the same equipment without need for transfer toadditional devices. In particular, the tablet coating system 100 asdisclosed may conduct processes requiring high humidity and elevatedtemperature conditions by redirecting airflow through the recirculatingair handler 106 as described herein above.

I. Recirculating Air Handler

In various aspects, a preexisting tablet coating system may be modifiedby incorporating a recirculating air handler 106 to supply air at anelevated temperature and elevated humidity beyond the capabilities ofexisting tablet coating systems. The incorporation of the recirculatingair handler 106 is accomplished without affecting the ability of themodified tablet coating system 100 to perform all of the functions ofthe preexisting tablet coating system. In various aspects describedherein below, the modified tablet coating system 100 is capable ofswitching between two operational modes: a preexisting mode in which thesystem 100 may perform all functions of the preexisting tablet coatingsystem and a humidification mode in which high humidity airflow isdelivered to the pan coater 102, thereby expanding the range ofconditions that may be maintained within the pan coater 102 by thesystem 100.

The tablet coating system 100 as disclosed is capable of maintaininghigh humidity conditions within the pan coater 102 without risk ofunwanted condensation through the inclusion of additional designfeatures associated with the recirculating air handler 106 as describedin detail herein below. Further, the recirculating air handler 106maintains a low pressure within the pan coater 102 relative to thesurrounding atmosphere to prevent the release of any contents of thetablet coating system 100, which may include noxious or bioactivecompounds.

In one aspect, the recirculating air handler 106 is capable of providingan airflow to the pan coater 102 that is maintained at a temperatureranging from about 50° C. to about 80° C. and at a relative humidity ofup to about 90%, including 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%,and 94%. This relative humidity level is well above the capability ofexisting tablet coating systems. Typical existing tablet coating systemsreduce the humidity within the pan coater element to avoid the formationof condensation and resulting degradation of tablet coating quality.

FIG. 4 is a schematic diagram illustrating the arrangement of componentsof a recirculating air handler 106 in one aspect. The recirculating airhandler 106 may receive exhaust air from the pan coater (not shown) viathe inlet duct 124; the flow rate of the exhaust air into therecirculating air handler 106 may be modulated by adjusting the speed ofthe recirculation blower 410. The recirculating air handler 106 mayinclude an inlet drain pan 406 to remove any condensation that may occurin this region as a result of condensation of the clean steam expandingthrough a vaporizer unit of the humidifier 420.

The recirculating air handler 106 may further include one or more inletfilters 408 to screen out any particulate matter within the airflow. Anyfilters known in the art may be selected for use as the one or moreinlet filters 408 without limitation. The one or more inlet filters 408may be selected based on any one or more factors including, but notlimited to: size distribution of particles to be removed from airflowand the acceptable degree of impedance of flow imparted by the one ormore inlet filters 408. In one aspect, the one or more inlet filters 408may include a prefilter 408A to screen out the larger particles whilepassing the finer particles, and a second filter 408 to screen out thefiner grains, as illustrated in FIG. 4 . In various aspects, any knownfilter device may be used as the second filter 408 without limitation.Non-limiting examples of filters suitable for use as a second filter 408include a HEPA filter and an ULPA filter.

The recirculating air handler 106 may further include an air blower 410to accelerate the airflow in an amount sufficient to maintain thedesired flow speed into the pan coater 102 as determined by sensorreadings and control algorithms described herein below. Any known blowerdevice may be selected for use as the air blower 410 without limitation.Non-limiting examples of suitable blower devices include axial flow fansand centrifugal fans. In an aspect, the speed of the air blower 410 maybe continuously varied by increasing or decreasing an electricalparameter including, but not limited to, a supply voltage or a supplycurrent.

Downstream of the air blower 410, the recirculating air handler 106 mayfurther include a vent 412 connecting the airflow within therecirculating air handler 106 to the external atmosphere. The vent 412may be controlled by a venting valve 414 which may opened in order toreduce pressure within the recirculating air handler 106 by an amountsufficient to maintain subatmospheric pressure within the tablet coatingsystem 100 to prevent the escape of noxious or bioactive compounds fromthe system 100 during use. In an aspect, the venting valve 414 may beautomatically actuated in response a control system command generatedusing measurements of pressure within the system 100 as described hereinbelow.

The recirculating air handler 106 may further include a heater 416situated downstream from the air blower 410 and vent 412. The heater 416may increase the air temperature by an amount sufficient to maintain thedesired air temperature within the pan coater 102. Any suitable type ofair heater known in the art may be selected for use as the heater 416without limitation including, but not limited to an electrical resistiveheater. The output of the heater 416 may be modulated by a controlsystem command generated using temperature measurements at one or morelocations throughout the system 100 including, but not limited to: theexit of the recirculating air handler 106, the supply duct 110 of thepan coater 102, the exhaust duct 108 of the pan coater 102, and anyother suitable location.

One or more exhaust filters 418 may be situated downstream of the airblower 410 and heater 416 to screen out any particulate matter withinthe airflow prior to humidification and delivery of the conditioned airto the pan coater 102. Any air filters known in the art may be selectedfor use as the one or more exhaust filters 418 without limitation. Theone or more exhaust filters 418 may be selected based on any one or morefactors including, but not limited to: size distribution of particles tobe removed from airflow and the acceptable degree of impedance of flowimparted by the one or more exhaust filters 418. In one aspect, the oneor more exhaust filters 418 may include a second HEPA or ULPA filter 418as illustrated in FIG. 4 .

A humidifier 420 may be situated within an exit region of therecirculating air handler 106 downstream of the one or more inletfilters 408, air blower 410, heater 416, and exhaust filter 418. Thehumidifier 420 may introduce clean steam into the airflow to increasethe humidity within the airflow to a level sufficient to maintain thedesired humidity within the pan coater 102, subject to one or moresystem constraints. In one aspect, the maximum humidity of the airflowdownstream of the humidifier may be sufficiently low to preventcondensation within the pan coater 102 or the ductwork connecting thepan coater 102 with the recirculating air handler 106. In one aspect,the humidifier 420 may introduce an amount of humidity into the airflowto result in a relative humidity in the airflow of up to about 90%,including 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, and 94%.

Any known humidifying device known in the art may be selected for use asthe humidifier 420 including, but not limited to: an evaporativehumidifier or a vaporizer. In one aspect, the humidifier 420 may be avaporizer. In this aspect, the vaporizer may be provided with cleansteam from a clean steam source 422 at a flow rate controlled by a steamvalve 424. The steam valve 424 may be automatically opened and closedusing a control signal generated using measured temperatures andhumidities at one or more locations within the pan coater 102 and ductsof the tablet coating system 100.

To remove any condensed water resulting from the treatment of theairflow by the humidifier 420, the recirculating air handler 106 mayfurther include a second drain pan 426 situated near the exit of therecirculating air handler 106. In one aspect, the second drain pan 426may extend slightly upstream of the humidifier 420 as well as downstreamof the humidifier 420, as illustrated in FIG. 4 .

As illustrated in FIG. 4 , the heated and humidified air may exit therecirculating air handler 106 via an exit duct 122 to be delivered tothe supply duct connected to the pan coater 102.

II. Control System and Sensors

In various aspects, the modifications to a preexisting tablet coatingsystem to produce the modified tablet coating system 100 of thisdisclosure may include one or more additional sensors to supplement theexisting sensors associated with the unmodified tablet coating system atvarious locations throughout the system. The additional sensors maysupplement the information obtained by the existing sensors, andinformation from all sensors may monitor the performance of therecirculating air handler 106 and may further provide feedbackmeasurements used to modulate one or more processes associated with theoperation of the recirculating air handler 106. Non-limiting examples ofprocesses associated with the operation of the recirculating air handler106 that may make use of the sensor measurements include: modulation ofairflow exiting the vent 412; speed settings of the air blower 410;temperature settings of the heater 416; and steam valve settings for thehumidifier 420.

In an aspect, illustrated in FIG. 6 , the modified tablet coating system100 may further include a control system 600 to control the operation ofvarious components and devices associated with the system 100. In oneaspect, the control system 600 may automatically control the operationof one or more components and devices using feedback that may includemeasurements from one or more sensors situated at various locationswithin the system 100. As illustrated in FIG. 6 , the control system 600may include a mode control 612 to coordinate the opening and closing ofvalves to switch the air supply of the pan coater 102 from theflow-through air handler 104 to the recirculating air handler 106 asdescribed herein previously. The control system 600 may further includea filter monitor 602 to monitor the operational status of the filters408 and 418 within the recirculating air handler 106 and issue warningsto the system user when a filter is clogged and/or in need of cleaningor replacement. In addition, the control system 600 may further includea V-stat 604 to modulate the air flow within the system 100, athermostat (T-stat) 606 to modulate the temperature within the system100, an H-stat 608 to modulate the humidity within the system 100, and aP-stat 610 to modulate the pressure within the pan coater 102 of thesystem 100.

Referring to FIG. 7 , the mode control 612 may control the opening andclosing of valves 112, 114, 116, and 118 to direct the airflow of thesystem 100 through the flow-through air handler 104 or the recirculatingair handler 106 as needed. In this aspect, the mode control 612 mayclose valves 114 and 116 to cut off air flow through the recirculatingair handler 106 and may open valves 112 and 118 to direct air flowthrough the flow-through air handler 104 and through the exhaust stack126 to implement the preexisting mode of operation of the system 100.The model control 612 may alternatively close valves 114 and 116 to cutoff flow-through air handler 104 and open valves 114 and 116 to directair flow through the recirculating air handler 106 to implement ahumidification mode of operation.

Pressure Sensors

In various aspects, pressure sensors may be incorporated at variouslocations throughout the tablet coating system 100 to monitor theoperational status of various system components and to providemeasurements used to modulate the operation of various systemcomponents. In particular, pressure measurements may be used by thecontrol system to maintain the air pressure within the pan coater 102 ata sub-atmospheric pressure to minimize the release of contents of thepan coater 102 to the atmosphere.

Referring to FIG. 7 , pressures may be measured by a first pressuresensor 702 situated on the interior of the pan coater 102 and a secondpressure sensor 704 situated within the external atmosphere and used bythe P-stat 610 to monitor the differential pressure to ensure that thepan coater pressure measured at sensor 702 is maintained below theatmospheric pressure measured at sensor 704 and to prevent the escape ofany airflow from the pan coater 102, which may include noxious orbioactive compounds. In this aspect, if the differential pressuremeasurement indicates that the pressure within the pan coater 102 risesabove a threshold pressure, the control system may command the ventingvalve 414 to open and relieve pressure within the system 100 until thedifferential pressure measurements indicate that the pressure measuredat sensor 702 within the pan coater 102 has fallen back below athreshold pressure. In an aspect, the differential pressure measurementsobtained by existing sensors may be integrated into the control systemassociated with the operation of the recirculating air handler 106. Inanother aspect, additional pressure sensors may be retrofitted to thepan coater 102.

The threshold pressure may be specified according to any criterion knownin the art. In an aspect, the threshold pressure may be provided as aratio of pressure within the pan coater 102 divided by the atmosphericpressure, wherein the ratio may range from about 0.95 to about 0.9995,including 0.95, 0.96, 0.97, 0.98, 0.99, 0.995, 0.999, and 0.9995. Inanother aspect, the threshold pressure may be provided as a differencein pressure calculated by subtracting the atmospheric pressure and thepressure inside the pan coater wherein the threshold pressure may be aminimum difference between the two pressures that may range from about0.15 inches water column to about 0.3 inches water column, correspondingto pressure difference ranging from about 0.005 psig to about 0.01 psig.In various aspects, the minimum difference between the two pressures maybe 0.15 inches water column, 0.175 inches water column, 0.2 inches watercolumn, 0.225 inches water column, 0.25 inches water column, 0.275inches water column, and 0.3 inches water column.

In another aspect, shown in FIG. 8 , the differential pressure between aregion upstream and downstream of each filter within the recirculatingair handler 106 may be monitored to assess the operational condition ofthe filter. As illustrated in FIG. 8 , pressure sensors 802 and 804 maymonitor the pressure upstream and downstream of a prefilter 408,respectively. Similarly, pressure sensors 806 and 808 may monitor thepressure upstream and downstream of a post-filter 418. Without beinglimited to any particular theory, as airborne particles accrue in afilter, the differential pressure upstream and downstream of the filtermay increase due to increased flow blockage within the filter. If thisdifferential pressure exceeds a threshold value, the control system 600may issue an alert to inform an operator of the system 100 that thefilter is fouled and in need of cleaning or replacement. The thresholdvalue in this aspect may be influenced by at least one factor includingbut not limited to: the size, thickness, and/or type of filter; the flowspeed through the filter, and any other relevant factor known in theart.

In yet another aspect, the pressure within the exit of the recycling airhandler 106 may be measured at pressure sensor 810 to monitor theoperation of the recycling air handler 106 and tablet coating system100. By way of non-limiting example, a sudden and significant rise inthe measured exit pressure may indicate a blockage in one or more of theducts or components of the tablet coating system 100.

Any appropriate pressure sensor known in the art may be selected for useas a pressure sensor in the tablet coating system 100. Non-limitingexamples of suitable pressure sensors include: piezoresistive sensors,capacitive sensors, piezoelectric sensors, optical sensors,potentiometric sensors, and any other suitable sensor known in the art.In an aspect, the pressure sensor may additionally incorporate aswitching mechanism for use with the control system to control thepressure within the pan coater 102 as described herein previously. Inthis aspect, the pressure sensor may further incorporate one or moreuser-definable set points connected to a switching mechanism.

By way of non-limiting example, the pressure sensor may incorporate auser-definable set point corresponding to the minimum allowabledifference between the pan coater pressure and the atmosphere. In thisexample, if the pressure difference falls below this set point, thepressure sensor may activate a switching mechanism that generates asignal used by the control system to open the venting valve 414 of therecirculating air handler 106.

Temperature Sensors

In various aspects, temperature within the pan coater 102 represents acritical process condition in many tablet coating processes that may besubject to extensive monitoring and control by the tablet coating system100. In processes conducted using heated and humidified air delivered bythe recirculating air handler 106, the control of temperature throughoutthe system 100 operating in humidification mode as illustrated in FIG. 3is critical to avoid condensation of water out of the air flow that maydegrade tablet quality. Without being limited to any particular theory,if the temperature of the airflow falls below the dew point of the air,condensation of water is likely to occur. Dew point, as describedherein, refers to the temperature at which the evaporation of water intothe air and the condensation of water from the air occur at equal rates.Thus, the temperature of the air flow at various locations throughoutthe system 100 may be measured to confirm that air temperature ismaintained above the dew point. In addition, temperature measurementsmay be used by the control system 600 to modulate the output of theheater 416 to increase or decrease the temperature of the air flowsupplied by the recirculating air handler 106 as needed.

In various aspects, temperature sensors may be situated throughout thesystem 100 to monitor the air flow temperature. Referring to FIG. 9 , inone aspect a temperature sensor 902 may be situated within the pancoater 102 to monitor the process conditions experienced by the tabletswithin the pan coater 102. In another aspect, temperature sensors 904and 906 may be situated within the inlet and exit of the recirculatingair handler 106, respectively, to monitor the temperature of the airentering and exiting the recirculating air handler 106.

In various other aspects, temperature sensors may be situated at one ormore locations within the system 100 to provide measurements used tocontrol the output of the heater 416 of the recirculating air handler106. In one aspect, a temperature sensor 912 may be situated justdownstream of the heater 416. In this aspect, if the temperature of theairflow measured at sensor 912 just downstream of the heater 416 exceedsa maximum temperature, the control system 600 may reduce the heat outputof the heater 416. In this aspect, the maximum temperature may beselected based on at least one factor including, but not limited to, theheat resistance of materials and devices within the recirculating airhandler 106 or a desired set point used to operate the tablet coatingsystem 100. In one aspect, the maximum temperature may be a temperatureset point used to modulate the output of the heater 416. In this aspect,the temperature set point may be specified by the system user and/orshifted upward or downward in order to achieve a desired temperaturemeasured by the additional temperature sensor 902 within the pan coater102.

In another aspect, a temperature sensor 908 may be situated within thesupply duct 110 of the pan coater 102 to measure the supply airtemperature and a second temperature sensor 910 may be situated withinthe exhaust duct 108 of the pan coater 102 to measure the discharge airtemperature as an additional means of monitoring the air temperaturewithin the pan coater 102 and the heat losses within the pan coater 102.The supply air temperature and/or the exhaust air temperature may alsobe used to modulate the amount of heat generated by the heater 416. Inone non-limiting example, if the supply air temperature and/or exhaustair temperature for the pan coater 102 falls below a predeterminedthreshold temperature, the control system may command increased heatoutput by the heater 416 by shifting the temperature set point describedherein above upward to a higher set point temperature. The predeterminedthreshold temperature may be selected based on at least one factorincluding, but not limited to: the desired temperature within the pancoater 102; the dew point of the air flow; and any combination thereof.In one aspect, the predetermined threshold temperature may be set tomaintain the air temperature of the pan coater 102 at a temperatureranging from about 50° C. to about 70° C. as desired, including 45° C.,46° C., 47° C., 48° C., 49° C., 50° C., 51° C., 52° C., 53° C., 54° C.,55° C., 56° C., 57° C., 58° C., 59° C., 60° C., 61° C., 62° C., 63° C.,64° C., 65° C., 66° C., 67° C., 68° C., 69° C., 70° C., 71° C., 72° C.,73° C., and 74° C.

Humidity Sensors

In various additional aspects, humidity sensors may be situated atvarious locations within the tablet coating system 100 to monitor thehumidity within the airflow of the system. Non-limiting examples ofsuitable sensor locations, as illustrated in FIG. 10 , include: ahumidity sensor 1004 situated within the pan coater 102; a humiditysensor 1006 situated within the inlet of the recirculating air handler106, and a humidity sensor 1002 situated within the exit of therecirculating air handler 106. In one aspect, the humidity measured bysensor 1002 at the exit of the recirculating air handler 106 may be usedby the control system 600 to modulate the water vapor introduced by thehumidifier 420.

Referring to FIG. 10 , a humidity sensor 1002 situated at the exit ofthe recirculating air handler 106 may be used to modulate the amount ofwater vapor introduced by the humidifier 420. Typically, the controlsystem 600 may open or close the steam valve 424 that controls the flowof clean steam from the clean steam source 422 in order to increase ordecrease the humidity of the air flow as needed. In one aspect, apreselected humidity set point may be used to modulate the humidifieroutput. In this aspect, if the measured humidity is above or below apreselected humidity set point, or if the measured humidity fallsoutside a minimum and maximum humidity level defined within an errorband of the desired humidity level, the control system 600 may increaseor decrease the humidifier output as needed.

In another aspect, the humidity may be measured by an additional sensor1004 situated within the pan coater 102. If the measured humidity atsensor 1004 exceeds a predetermined condensation threshold, the controlsystem 600 may command the reduction of clean steam flow entering thehumidifier 420 by closing the steam valve 424. The predeterminedcondensation threshold may be selected to be a humidity level at whichcondensation is likely to occur within the pan coater 102. In oneaspect, the threshold level may be selected to maintain the dew point atleast 10° C. below the temperature of the airflow. In various otheraspects, the threshold level may be selected to maintain the dew point10° C., 11° C., 12° C., 13° C., 14° C., 15° C., 16° C., 17° C., 18° C.,19° C., 20° C., 25° C., and 30° C. below the temperature of the airflow.In various other aspects, the threshold level may be selected tomaintain the dew point at least 7° C., 8° C., 9° C., 10° C., 11° C., 12°C., 13° C., 14° C., 15° C., 16° C., 17° C., 18° C., 19° C., 20° C., 25°C., and 30° C. below the temperature of the airflow.

Without being limited to any particular theory, dew point depends on acombination of environmental conditions including, but not limited to,atmospheric pressure and moisture content of the air. Without beinglimited to any particular theory, at a constant pressure the dew pointis proportional to the moisture content of the air. For example, anincrease in humidity in the air corresponds to a higher dew point. Thehumidity measurement used by the control system 600 in this aspect maybe obtained by the humidity sensors in terms of dew point or the controlsystem 600 may calculate dew point based on measured humidity andatmospheric pressure using methods known in the art. In another aspect,if the dew point rises to within 5° C. below the temperature of theairflow, the control system 600 may completely shut down the humidifieroutput until the dew point falls to a level at which no risk ofcondensation within the pan coater 102 is likely. In various otheraspects, the control system 600 may completely shut down the humidifieroutput if the dew point rises to within 0.5° C., within 1° C., within 2°C., within 3° C., within 4° C., within 5° C., within 6° C., within 7°C., within 8° C., within 9° C., within 10° C., within 15° C., or within20° C. below the temperature of the airflow.

Air Flow Sensors

In various other additional aspects, air flow sensors may be situated atone or more locations within the tablet coating system 100 to monitorflow speed within the system 100. Referring to FIG. 11 , in one aspectan air flow sensor 1102 may be situated within the exit of therecirculating air handler 106 and the air flow measurements may be usedto modulate the output of the air blower 410 in order to achieve adesired air flow. Typically, the control system 600 may increase ordecrease the power, current, and/or voltage supplied to the motor of theair blower 410 in order to increase or decrease the air flow as needed.In one aspect, a preselected air flow set point may be used to modulatethe motor speed of the air blower 410. In this aspect, if the measuredair flow is above or below a preselected air flow set point, or if themeasured air flow falls outside a minimum and maximum air flow within anerror band of the desired air flow level, the control system 600 mayincrease or decrease the air blower output as needed.

In another aspect, additional air flow sensors may be situated at otherlocations within the tablet coating system 100 to monitor air flowthroughout the system 100. Non-limiting examples of additional air flowsensors include a sensor 1106 situated within the supply duct 110 and/ora sensor 1104 situated within the exhaust duct 108 of the pan coater102.

III. Method of Generating High Humidity Conditions Using Tablet CoatingSystem

As described herein previously, the recirculating air handler 106 may beintegrated into the preexisting components of the preexisting tabletcoating system so as to retain full functionality of the preexistingtablet coating system. Typically, the preexisting tablet coating systemdirects airflow through the flow-through air handler 104 in apreexisting mode. Thus, the modified tablet coating system 100 mayoperate in this preexisting mode to perform a variety of proceduresassociated with the production of coated tablets including preheatingtablets, applying one or more coating compositions to the tablets, anddrying the tablets. In this preexisting mode, the temperature within thepan coater 102 may be maintained at a temperature of about 70° C. orabove, including 70° C., 72° C., 74° C., 76° C., 78° C., 80° C., 85° C.,90° C., 100° C., 120° C., 140° C., 160° C., 180° C., and 200° C. Also inthe preexisting mode, conditions within the pan coater 102 may bemaintained at a dew point ranging from about 10° C. to about 15° C.,including 10° C., 11° C., 12° C., 13° C., 14° C., and 15° C.

In various aspects, the tablet coating system 100 described hereinpreviously may be operated in a humidification mode to provide humidprocess conditions within the pan coater 102 that are characterized by atemperature from about 50° C. to about 70° C., including 50° C., 52° C.,54° C., 56° C., 58° C., 60° C., 62° C., 64° C., 66° C., 68° C., and 70°C. In addition, process conditions in the humidification mode may becharacterized by relatively high humidities corresponding to a dew pointranging from about 45° C. to about 70° C., and more specifically a dewpoint ranging from about 45° C. to about 55° C., including dew points of45° C., 46° C., 47° C., 48° C., 49° C., 50° C., 52° C., 54° C., 56° C.,58° C., 60° C., 62° C., 64° C., 66° C., 68° C., and 70° C. In furtheraspects, the tablet coating system 100 described herein previously maybe operated in a humidification mode to provide humid process conditionswithin the pan coater 102 that are characterized by relatively highhumidities corresponding to a dew point within the range from about 45°C. to 50° C., 48° C. to 52° C., or 49° C. to 54° C. In even furtheraspects, the tablet coating system 100 described herein previously maybe operated in a humidification mode to provide humid process conditionswithin the pan coater 102 that are characterized by relatively highhumidities corresponding to a dew point within the range from about48.5° C. to 49.5° C., 49.5° C. to 50.5° C., or 50.5° C. to 51.5° C.Optionally, the dew point in the humidification mode may be a constantdew point. The tablet coating system 100 and methods of the presentinvention described herein may provide the advantage of utilizing ahigher constant dew point than the prior art, without condensationoccurring. The ability to provide humid conditions as described hereinwithout condensation occurring is significant because it prevents thetablets from dissolving or losing structural integrity. In oneembodiment, lack of condensation may be established when the dew pointis maintained at least at least 10° C. below the temperature of theairflow. Typically, these humid process conditions may be provided asone stage of a procedure carried out by the tablet coating system 100 toproduce a batch of coated tablets. In one aspect, a method of providinghumid process conditions may include establishing the air flow of thetablet coating system 100 through the recirculating air handler 106,introducing humidity into the airflow for a desired process duration,and subsequently redirecting the air flow of the system back through theflow-through air handler 104 to reconfigure the tablet coating system100 back into the preexisting mode for subsequent process steps.

FIG. 5 is a flow chart illustrating a method 500 of providing humidprocess conditions within the tablet coating system 100 described hereinabove using the recirculating air handler 106. The method 500 includesconfiguring the tablet coating system 100 to direct airflow through therecirculating air handler 106 at step 502. In step 502, the airflowpattern is altered from the pattern illustrated in FIG. 2 , in which theair flow passes through the flow-through air handler 104, to the patternillustrated in FIG. 3 , in which the air flow passes through therecirculating air handler 106.

In an aspect, step 502 includes shutting down the airflow through theflow-through air handler 104. In this aspect, valve 112 may be closed toprevent the exit of air flow through the flow-through air handler 104and valve 118 may be closed to prevent the flow of exhaust air out ofthe exhaust stack 126. In addition, the components of the flow-throughair handler 104 may be deactivated to shut down the operation of theflow-through air handler 104. Non-limiting examples of components of theflow-through air handler 104 include an air blower, an air heater, and adehumidifier.

The method 500 at step 502 further includes establishing the airflowthrough the recirculating air handler 106. In this aspect, valve 116 maybe opened to allow exhaust air from the pan coater 102 to pass into therecirculating air handler 106. In addition, the valve 114 may be openedto allow air flow to exit the recirculating air handler 106 an pass intothe pan coater 102. In addition, the air blower 410 and heater 416 ofrecirculating air handler 106 may be activated to establish the desiredtemperature and flow rate appropriate for the humidifying step to beconducted within the pan coater 102. At step 502 and all subsequentsteps, the pressure within the pan coater 102 is maintained at pressurethat is at least about 0.15 inches of water column below the atmosphericpressure as described herein above, including 0.15 inches of watercolumn, 0.2 inches of water column, 0.25 inches of water column, 0.3inches of water column, 0.35 inches of water column, 0.4 inches of watercolumn, 0.45 inches of water column, 0.5 inches of water column, 0.75inches of water column, and 1 inch of water column below the atmosphericpressure.

The method 500 may further include preheating the ductwork and pancoater 102 of the tablet coating system 100 at step 504. By preheatingthe ductwork prior to the introduction of additional humidity into theairflow, condensation of water from the airflow may be inhibited. Instep 504, the heater 416 and air blower 410 of the recirculating airhandler 106 may be operating with the humidifier 420 disabled until theductwork and pan coater 102 of the system 100 are determined to be fullyheated. In one aspect, measurements from temperature sensors situatedthroughout the system 100 may be monitored to assess the heating of theductwork. For example, if the temperature measurements are determined tobe stabilized at essential values, the ductwork may be determined to beheated. In another example, if the difference in measured temperature ofthe airflow within the supply duct 110 and exhaust duct 108 isdetermined to be less than a predetermined threshold, the ductwork maybe determined to be heated. The humid conditions may be maintainedwithin the pan coater 102 for the duration of the humidification phaseof the tablet coating procedure as needed.

The method 500 may further include establishing the humid conditionswithin the pan coater 102 at step 506. In this step, the humidifier 420of the recirculating air handler 106 may be activated by opening thesteam valve 424. Initially, the humidity may be introduced slowly andramped up to the desired value of humidity within the pan coater 102.The temperature and dew point within the pan coater 102 may be monitoredand used to adjust the output of the humidifier 420 during use. Inaddition, temperature and dew point may be monitored at other locationswithin the system 100 including, but not limited to, the inlet 124 andexit 122 of the recirculating air handler 106 to assess the likelihoodof condensation forming anywhere in within the system 100 during use.

In various aspects, the humid conditions within the pan coater 102 maybe established and maintained at conditions that prevent condensationfrom occurring anywhere within the system 100 during use. In one aspect,condensation and also lack of condensation may be assessed by visualinspection of the ducts and devices of the system 100 including but notlimited to: the pan coater 102, the supply duct 110, the exhaust duct108, and the recirculating air handler 106. In another aspect,condensation may be inferred by the detection of an air temperaturewithin any duct or device of the system 100 that is less than about 10°C. above the measured dew point at any location within the system 100,including less than 5° C., 6° C., 7° C., 8° C., 9° C., 10° C., 11° C.,12° C., 13° C., 14° C., and 15° C. above the measured dew point.

Typically, the humidity may be introduced in an amount that maintainsthe measured temperature at least about 10° C. above the measured dewpoint at any location within the system 100, including 10° C., 15° C.,20° C., 25° C., 30° C., 40° C., 50° C., 60° C., 80° C., and 100° C.above the measured dew point. In one aspect, a warning may be issued ifthe measured temperature is within about 10° C. of the measured dewpoint at any location within the system 100, including within 5° C., 6°C., 7° C., 8° C., 9° C., 10° C., 11° C., 12° C., 13° C., 15° C., and 15°C. of the measured dew point at any location within the system 100. Inanother aspect, the system 100 may shut down the humidifier 420 if themeasured temperature is within about 5° C. of the measured dew point atany location within the system 100, including within 2.5° C., 3° C., 3.5C, 4° C., 4.5° C., 5° C., 5.5° C., 6° C., 6.5° C., 7° C., and 7.5° C. ofthe measured dew point at any location within the system 100. The humidconditions may be maintained within the pan coater 102 for the durationof the humidification phase of the tablet coating procedure as needed.

Upon completion of the humidification phase, the method 100 may furtherinclude lowering the humidity within the pan coater 102 to end thehumidification phase of the tablet coating procedure. To this end, themethod 100 may further include clearing the humidity from the pan coater102 at step 508. In this step, the humidifier 420 may be deactivated byfully closing the steam valve 424 while maintaining the air temperatureand flow rate within the system 100. In addition, the pressure withinthe pan coater 102 may be lowered slightly and maintained at a pressureof about 0.5 inches of water column below atmospheric pressure tofacilitate the removal of humidity from the airflow, including 0.1inches of water column, 0.2 inches of water column, 0.3 inches of watercolumn, 0.4 inches of water column, 0.5 inches of water column, 0.6inches of water column, 0.7 inches of water column, 0.8 inches of watercolumn, 0.9 inches of water column, and 1 inch of water column belowatmospheric pressure. The humidity may be monitored at various locationswithin the system 100 to assess the amount of humidity remaining withinthe system 100. In one aspect, the humidity may be determined to beremoved from the system 100 when the measured dew point falls below athreshold value that may be about 15° C., including 10° C., 11° C., 12°C., 13° C., 14° C., 15° C., 16° C., 17° C., 18° C., 19° C., and 20° C.

Once the humidity is cleared from the pan coater 102 and othercomponents of the system 100, the method 100 may further includeredirecting system airflow back through the flow-through air handler 104at step 510. In this step the air blower 410 and heater 416 may bedeactivated to fully shut down the recirculating air handler 106. Inaddition, valves 114 and 116 may be closed to prevent airflow fromentering or exiting the recirculating air handler 106. In addition,valve 112 may be reopened to allow the delivery of air flow from theflow-through air handler 104 to the pan coater 102. Further, valve 118may be opened to allow the exhaust from the pan coater 102 to ventthrough the exhaust stack 126. Upon completion of step 510, the tabletcoating system 100 may function in the preexisting mode in a mannersimilar to the most existing tablet coating systems.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims. Those of skill inthe art should, however, in light of the present disclosure, appreciatethat many changes could be made in the specific embodiments that aredisclosed and still obtain a like or similar result without departingfrom the spirit and scope of the invention, therefore all matter setforth herein is to be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. A method of supplying a humid air flow to a pancoater of a tablet coating system, the method comprising: providing thepan coater to apply one or more coatings to a tablet; providing arecirculating air handler operably connected to the pan coater, therecirculating air handler comprising: an inlet duct operable to receiveexhaust air from the pan coater; a humidifier to introduce moisture intothe exhaust air in an amount resulting in an exit air having a relativehumidity of up to about 94%; a vent operable to release air from therecirculating air handler to the atmosphere via a vent valve, whereinthe vent valve is opened as needed to maintain a pressure within the pancoater of at least 0.15 inches of water column below atmosphericpressure; and an exit duct operable to deliver the exit air to the pancoater; one or more configurable valves; and a control system comprisinga mode control operable to coordinate opening and closing of the one ormore configurable valves to switch an air supply of the pan coater froma flow-through air handler to the recirculating air handler.
 2. Themethod of claim 1, further comprising: establishing an air flow throughthe recirculating air handler operatively connected to receive exhaustair flow from the pan coater and to deliver a supply air flow to the pancoater; heating the air flow to pre-heat the pan coater, a supply ductdelivering air flow to the pan coater from the exit duct, and an exhaustduct receiving the exhaust air from the pan coater and delivering theexhaust air to the inlet duct; establishing and maintaining a humid airflow within the pan coater for a duration of a humidification process;and clearing the humid air flow from the pan coater.
 3. The method ofclaim 2, wherein the air flow is heated to a temperature ranging fromabout 50° C. to about 80° C. and a dew point ranging from about 45° C.to about 55° C.
 4. The method of claim 2, wherein the humid air flow iscleared from the pan coater by deactivating the humidifier andmaintaining a pressure within the pan coater that is at least 0.25inches of water column below atmospheric pressure.
 5. The method ofclaim 2, further comprising: reestablishing air flow through theflow-through air handler operatively connected to the supply duct andconfigured to receive external air from the atmosphere, whereinreestablishing air flow through the flow-through air handler comprisesclosing a first and second valve operable to block flow entering andexiting the recirculating air handler, opening a third valve operable todirect air flow from the flow-through air handler into the supply duct,and directing the exhaust air flow from the pan coater through anexhaust stack into the atmosphere.
 6. The method of claim 2, furthercomprising: removing particulate matter from an airflow entering therecirculating air handler via at least one inlet filter in therecirculating air handler situated upstream of the humidifier; removingparticulate matter from an airflow exiting the pan coater via at leastone exit filter situated downstream of the humidifier; monitoring anoperational status of the at least one inlet filter or at least one exitfilter via a filter monitor in the control system; and issuing warningsto a system user when a filter is clogged and/or in need of cleaning orreplacement.
 7. The method of claim 1, wherein the control system isfurther operable to modulate the air flow within the system, modulatetemperature within the system, modulate humidity within the system,and/or modulate pressure within the pan coater.
 8. The method of claim1, further comprising: heating the pan coater via a heater; measuringthe temperature of the air flow downstream of the heater via atemperature sensor, wherein the control system reduces the heat outputof the heater if the temperature of the air flow exceeds a maximumtemperature; and measuring air temperature within the pan coater via atemperature sensor, wherein the control system is operable to commandincreased heat output by the heater if the air temperature for the pancoater falls below a predetermined threshold temperature.
 9. The methodof claim 1, further comprising: measuring humidity introduced by thehumidifier via a humidity sensor and an additional humidity sensor, thehumidity sensor operatively connected to the exit duct of therecirculating air handler, wherein the control system is operable toincrease or decrease the humidifier output if the measured humidityfalls outside a minimum or maximum humidity level, and wherein thecontrol system is operable to reduce clean steam flow entering thehumidifier if the measured humidity at the additional humidity sensorexceeds a predetermined condensation threshold.
 10. The method of claim1, further comprising: monitoring a differential pressure between afirst pressure sensor and a second pressure sensor, wherein the controlsystem issues an alert or opens the vent valve if the differentialpressure exceeds a threshold value.
 11. The method of claim 10, whereinthe first pressure sensor is inside the pan coater and the secondpressure sensor is within external atmosphere.
 12. The method of claim10, wherein the first pressure sensor is upstream of a filter and thesecond pressure sensor is downstream of the filter.
 13. The method ofclaim 1, further comprising: supplying a low humidity air flow to thepan coater via the flow-through air handler, wherein the low humidityair flow has a relative humidity less than the humid air of therecirculating air handler.
 14. The method of claim 1, wherein the one ormore configurable valves is configured to: cut off flow through therecirculating air handler and direct the air flow from the flow-throughair handler to a supply duct of the pan coater and from an exhaust ductof the pan coater to an exhaust stack; or cut off flow from theflow-through air handler and direct the air flow from exit duct of therecirculating air handler to the supply duct of the pan coater and fromthe exhaust duct of the pan coater to the inlet duct of the flow-throughair handler.